The present invention is directed to an improvement to treatment plans using brachytherapy or the like and more specifically to a technique for rapid and accurate identification and quantification of needle placement departures from such a treatment plan.
In the treatment of prostate cancer, a method is often employed to implant numerous radioactive seeds in a carefully preplanned pattern in three dimensions within the prostate. That procedure serves to deliver a known amount of radiation dosage concentrated around the prostate, while at the same time sparing radiation-sensitive tissues, such as the urethra, the bladder and the rectum. Customarily, 60 to 120 seeds are placed through 15 to 30 needles in the inferior (feet) to superior (head) direction. Those needle positions are selected from a 13xc3x9713 grid of 0.5 cm evenly spaced template holes, which are used to achieve precise needle insertion. The number of those holes which intersect with the prostate cross section, and therefore are potentially usable, is typically about 60. The number of mathematical combinations is therefore greatly in excess of 1016, each of which is a potential treatment plan but is associated with different degrees of cancer control and a different likelihood of treatment complications.
In current clinical practice, the design of a suitable seed configuration which is customized to the anatomy of a patient is achieved by a highly trained medical physicist or dosimetrist by using trial-and-error manual iterations. The practitioner usually starts with an initial needle configuration based on experience or rules of thumb, and then adjusts the radioactive strength per seed or the locations of certain needles or both until the calculated dose intensity distribution satisfies a set of clinical considerations. That process requires between 15 minutes and 2 hours, depending on the experience of the treatment planner and the geometric complexity of the relationship between the prostate and the surrounding anatomical structures.
Those known treatment planning processes are typically aided by one of several available commercial computerized treatment planning systems. Such treatment planning systems enable the user to outline the prostate in relation to a template grid, to turn on or off any available needle positions and seed positions within each needle, and to examine the resultant dose distribution in two or three dimensions. Examples of such planning systems include those offered by Multimedia Medical Systems (MMS) of Charlottesville, Va., SSGI Prowess, of Chico, Calif., Nucletron Plato, from Columbia, Md., Computerized Medical Systems (CMS) Focus, of St Louis, Mo., Radiation Oncology Computer Systems (ROCS), of Carlsbad, Calif., ADAC Laboratory""s Pinnacle, of Milpitas, Calif. and Theraplan, available from Theratronics International Ltd. of Kanata, Ontario, Canada.
In a number of such known commercial treatment planning systems, for example, those available from MMS and SSGI, the initial needle configuration that otherwise would have to be turned on by the human treatment planner is automatically set up by the computer system. That initial setup is based on simple rules of thumb, such as uniform loading, peripheral loading or modified peripheral loading. In a number of instances, the manufacturer claims that its planning system offers xe2x80x9cautomatic planningxe2x80x9d, xe2x80x9cgeometric optimizationxe2x80x9d, or xe2x80x9creal-time dosimetryxe2x80x9d. However, none of those commercial planning systems offer true optimization in that the automatically loaded seeds are not designed based on customized dosimetric calculations. Rather, they are designed to fill the space of the prostate in some predetermined manner. Therefore, such known automatic seed loading techniques are designed to save between 15 and 30 mouse clicks by the operator (or about 1 minute of operation). However, the user is still required to apply his or her expert knowledge to iteratively improve upon that initial design in order to achieve customized planning for any individual patient. Thus, there are two significant drawbacks of the above-mentioned current techniques: First, the complete treatment planning process is under the manual guidance of a radiation planning expert using trial and error techniques; and second, the adjustment of the delivered dose is achieved by varying the radioactive strength per seed until an isodose surface with the desired shape and size is scaled up or down to the prescription dose, i.e., those techniques will suffer when the activity per seed is fixed, as at the time of surgical implantation in the operating suite.
Because of those two severe drawbacks, the currently available commercial treatment planning systems are not suitable for intraoperative treatment planning in the surgical suite, where the patient is placed under anesthesia in volatile conditions and where the cost per minute is very high. The variability of human performance, experience and stress, and the general inability of humans to manage large amounts of numerical data in 1 to 2 minutes are also factors that deter current practitioners from performing intraoperative treatment planning.
An optimization technique for treatment planning is taught by U.S. Pat. No. 5,391,139 to Edmundson. More specifically, Edmundson is intended for use with a high dose rate (HDR) source which is moved within a hollow needle implanted in a prostate or other anatomical portion. The medical personnel using the system of Edmundson select a needle location using empirically predetermined placement rules. An image is taken of the prostate with the hollow needles implanted in it, and the dwell time of the source at each dwell position in the needle is optimized. However, placement itself is not optimized, but must instead be determined by a human operator.
Another optimization technique is taught by WO 00/25865 to one of the inventors of the present invention. An implant planning engine plans implants for radiotherapy, e.g., prostrate brachytherapy. The system optimizes intraoperative treatment planning on a real-time basis using a synergistic formulation of a genetic algorithm, multi-objective decision theory and a statistical sensitive analysis.
While the above techniques allow calculation of optimized dwell time, placement or the like, they do not provide for detection and correction of errors in needle or seed placement.
It will be apparent from the above that a need exists in the art to detect and correct errors in implementation of a treatment plan.
It is therefore a primary object of the present invention to permit rapid and accurate identification and quantification of needle placement departures from a treatment plan generated prior to a brachytherapy implant based on real-time ultrasound.
It is another object of the invention to allow real-time correction to the brachytherapy dosimetry and iterative compensation of loss of dose coverage due to misplacement of the needles/catheters and seeds.
It is still another object of the invention to permit such identification, quantification and correction without the need for CT or MR imaging during the interval between needle/catheter placement in the target organ and final deposition of radioactive sources for irradiation of the target organ.
To achieve the above and other objects, the present invention is directed to a technique for identifying and quantifying needle displacement departures from a placement plan for the placement of radioactive seeds in a prostrate or other internal organ for brachytherapy or the like. The placement plan is made available to an intraoperative tracking interface which also shows a live ultrasound image of the needle or catheter placement in the prostate. The difference in the x-y plane between the planned and actual locations of the needle or catheter is calculated, and from that difference, the error in position of each seed is calculated. The seeds are moved, or the operator changes the number of seeds, and the dose is recalculated. A small column of ultrasound images is taken, and each seed located in the column of images is given a confidence level. If the confidence level exceeds a threshold set by the operator, the dosimetry is recalculated. Periodically throughout the seed placement, fluoroscopic x-rays are taken, and the seed coordinates are matched to the x-ray image. Seed locations with low confidence levels are adjusted based on the x-ray locations, and the dosimetry is recalculated.
In a preferred embodiment, the technique is carried out through the following steps.
1. The needle/catheter placement plan is made available to an intraoperative tracking interface. That interface contains an electronic worksheet of needle and seed coordinates, a live ultrasound image window into which real-time video image of needle/catheter placement is fed, and a series of isodose dosimetry panels reflecting the current state of dose coverage. Each of the needles/catheters can be activated by highlighting the corresponding row in the coordinates worksheet, or by highlighting the corresponding grid location graphically.
2. Following insertion of each needle/catheter, a hyperechoic (i.e., bright) spot appears on the live ultrasound image. That location is manually identified by the operator. The difference in the x-y plane between the planned location and the actual location of the needle/catheter is calculated to give errors xcex94x and xcex94y. The errors xcex94x and xcex94y are then reflected on the grid location. The errors of each seed, xcex94xxe2x80x2 and xcex94yxe2x80x2, are calculated based on straight line interpolation at the planned z location of the seed; the said straight line is constructed by joining two known points: (a) the actual needle location shown on ultrasound at the known z plane, (b) the template coordinate outside the patient body, through which the needle is inserted under precision template guidance (therefore at that location xcex94x and xcex94y shall be assumed to equal zero). The dose is then recalculated by moving the seeds along the activated needle/catheter in x and y by amounts xcex94xxe2x80x2 and xcex94yxe2x80x2, which may be the same or different for each and every seed. The dosimetry updated by such feedback of seed placement errors is redisplayed on the series of isodose panels.
In addition, the operator is permitted to change the number of seeds deposited by the needle/catheter in question. In that case, the operator is required to enter the seed locations along the needle/catheter, which overrides the original treatment plan. Seed placement errors in such a case are tracked identically to the procedure described above.
3. A small column of ultrasound images in 3D is acquired along the straight line as constructed above. That column can be perpendicular to the x-y plane, or in fact may often sustain an angle xcex1 and an angle xcex2 from the x and the y planes, respectively. The exact number of seeds as deposited is identified using image processing algorithms in that column of 3D ultrasound region of interest. Each seed identified in that manner is assigned a confidence level, which depicts the likelihood/uncertainty of seed localization. The size of that column is initially set small; if the total number of seeds found in that manner is not equal to the number of seeds deposited by the given needle/catheter, the width of the column is adjusted (e.g., the width is increased to find additional seeds).
Whereas the previous step quantifies the errors xcex94xxe2x80x2 and xcex94yxe2x80x2 for each seed, the ultrasound step quantifies xcex94zxe2x80x2 for each seed and at the same time further corrects xcex94xxe2x80x2 and xcex94yxe2x80x2. If the confidence level of a given seed""s localization exceeds a threshold value (to be set by the operator), the dosimetry is re-calculated yet again using the updated seed location and displayed in the same isodose panels. The isodose calculated is assigned a confidence level, which is a numerical composite of the individual confidence levels of the seeds and the dosimetric impact of positional uncertainties at each seed location (e.g., in high dose region, positional uncertainty has low impact).
4. Periodically throughout the seed placement procedure and the end of seed placement, a fluoroscopic x-ray may be may be taken in the anterior-posterior direction and at up to xc2x145 degrees on either side of the anterior-posterior directions. The seed coordinates as determined above are projected in the same orientations. A best match to the x-ray seed projections is made based on multiple point matching using those seed identifications with the highest confidence levels. Subsequent to such matching, the seed locations with low confidence levels are adjusted based on the x-ray locations. As a result, the confidence levels of those latter seeds are increased by a amount reflective of the best match quality. The dosimetry is recalculated. The confidence level of the dosimetry is updated using updated confidence levels of the seeds.